This invention relates to a slip element for use in connection with a downhole tool for use in wellbores in oil and gas recovery operations.
In the drilling or reworking of oil wells, it is often desirable to seal casing, or seal tubing or other pipes in the casing, to isolate a zone in the casing, and, to this end, downhole sealing tools, such as bridge plugs, frac plugs; and packers are utilized. These tools typically employ a slip assembly consisting of a plurality of slip elements mounted on a mandrel, or the like, that are initially retained in close proximity to the mandrel but are forced outwardly away from the mandrel upon the tool being set to engage, or grip, the inner wall of the casing. This locates and secures the tool in the wellbore so that sealing, and other wellbore operations, may be performed.
Some of these slip elements are made with cast iron so that they will readily grip the inner wall of the casing when expanded. However, these cast iron slip elements are relatively heavy and, as a result, have often been replaced with composite slip elements fabricated, at least in part, of a relatively lightweight plastic material. However, the composite slip elements often cannot properly grip the inner casing wall. Therefore, ceramic inserts, or buttons, have been placed in the composite slip elements to bite into the inner casing wall to assist in the gripping action discussed above. Another advantage of the ceramic inserts is that when the tool is no longer needed, the ceramic inserts are easy to drill or mill out with the slip elements when the tool is to be destructively removed from the wellbore. However, the ceramic inserts tend to chip, especially when they are set in the casing, which can compromise the gripping action of the slip elements.
Metallic inserts have been used in place of the ceramic inserts since they do not chip. However, when the tool is to be removed from the wellbore, it is often drilled or milled out, and it is often difficult to drill or mill out the metallic inserts.
Thus, there remains a need in the art for a cost-effective slip assembly that includes inserts that grip the casing wall, yet resist chipping and can easily be drilled or milled out.